1. Field of the Invention
This invention relates generally to racks for supporting articles during the plating thereof, and more particularly is directed to a coating for such racks intended to be used for supporting electrically non-conductive articles during the chemical or electroless plating thereof and also, if desired, during a subsequent further electroplating of the supported articles.
2. Description of the Prior Art
When an article of an electrically non-conductive material, for example, a plastic resin, glass, porcelain, ceramic or the like, is to be plated, such article is supported or suspended from a rack and, while thus suspended, is subjected to an electroless or chemical plating process for depositing a metal layer on the surface of the article, whereupon, if desired, the article may be subjected to a further electroplating process for depositing an additional metal layer thereon from an electrolyte. The racks used for supporting articles during the electroplating thereof are usually formed of metal, such as, copper, stainless steel or the like, covered with a resin paint coating, for example, of polyvinyl chloride, polyethylene, polyester, polyurethane or the like, so that the plating metal will not be deposited on the rack itself during the electroplating process. However, if such racks are used for supporting non-conductive articles during the chemical or electroless plating thereof, as aforesaid, the coated surface of the rack is activated during the activating treatment to which the suspended non-conductive articles are subjected as a prelude to the chemical or electroless plating process. Therefore, the electroless plating process deposits metal on the coated surface of the rack as well as on the non-conductive article or articles suspended therefrom. If the electroless plating process is followed by an electroplating process to further plate the non-conductive articles while suspended from the same rack, then the surface of the rack is also electroplated.
It will be apparent that the deposit of plating materials on the rack during the electroless plating of non-conductive articles suspended therefrom and during the subsequent electroplating of such articles constitutes a waste of such plating materials. Further, if the coated rack supporting the non-conductive articles during the electroplating thereof has had its surface plated with metal during the preceding electroless plating process, such metal plating on the rack causes non-uniform current distribution which results in deterioration of the electroplating of the suspended articles, particularly at concave portions of the latter.
In view of the foregoing, it has been the practice in plating non-conductive articles to manually transfer the latter from the rack supporting the same during the initial electroless plating to another coated rack whose surface is not plated with metal and from which the articles are then suspended during the subsequent electroplating process. However, it is obvious that a substantial waste of labor is involved in manually transferring the articles from one rack to another intermediate the electroless and electroplating processes. Further, the need to transfer the articles from one rack to another makes it impossible to carry out the entire plating operation by means of a fully automated or conveyor system.
With the foregoing arrangement, the racks used during the electroless plating of the non-conductive articles usually have the deposited metal removed therefrom by means of nitric acid. However when the deposited metal is thus dissolved, gaseous nitrogen oxides, such as, nitrogen monoxide and dioxide, are generated and these nitrogen oxides are toxic to humans and must be specially treated.
In order to avoid the foregoing problems, it has been proposed to provide racks used for supporting non-conductive articles during the plating thereof with a plastic resin coating which contains one or more metal oxides, for example, oxides of cadmium, antimony, lead or the like, and/or to treat such racks with a liquid or gaseous halide prior to the electroless plating process so as to avoid deposition of metal on the rack surface during such plating process. However, such metal oxides are generally insoluble in organic solvents, so that it is difficult to uniformly disperse the metal oxide in the plastic coating material for reliably ensuring that metal will not be deposited on the coated surface of the rack during the electroless plating of articles suspended therefrom. Further, the described gaseous halides are very toxic to humans so that the treatment of racks therewith requires the use of expensive exhaust and treating devices.